First known as the LRIX (long-range interceptor,
experimental), development of the XF-108 followed USAF GOR 114, dated 6 October
1955. The North American letter contract of 6 June 1957 called for an
all-weather, two-man, two-engine, long-range interceptor, with a combat speed of
at least Mach 3 and swift maneuver at 70,000 feet. The aircraft would carry two
or more air-to-air missiles with nuclear or conventional warheads. The armament
bay was to house a number of weapon combinations.

The Air Force expected a lot from the complex new plane.
Many subcontractors were involved. Hughes Aircraft Corporation would provide the
aircraft's fire-control system and GAR-9 missiles; Convair, the wing, Marquardt,
the air induction control system; Hamilton Standard, the air conditioning and
pressurization; Federal Division of the International Telephone & Telegraph Co.,
the mission and traffic control system; and Electronic Specialty Co., the
antenna system. The Air Force would take care of the engine, the General
Electric J-93 turbojet (first developed as the X-279E). It wanted an early 1963
operational date, 1,000-nm cruise speed with 5 minutes of combat at Mach 3, and
a cruise speed of Mach 3 for 350-nm and 10 minutes of combat time (also at Mach
3). Finally, the F-108 should be able to fly to a specified point at supersonic
speed, loiter for about an hour, and speed on to the target.

A mockup inspection on 26 January 1959 disclosed few needed
changes. Nonetheless, the XF-108 (nicknamed the Rapier on 15 May 1959) never
flew. The Air Force in 1957 had programmed for more than 480 F-108s, but the
pinch in funds wiped out the whole project on 23 September 1959. The Air Force
believed the F-108 would have been a good mobile missile launcher to intercept
enemy aircraft far away from their intended targets. This was a role the B-70
bomber (being also built by North American and later consigned to the XF-108's
fate) could not perform. Total RDT&E expenditures then stood at $141.9 million.

North
American F-108A "Rapier"

Click on Picture to enlarge

The North American F-108 was designed as a very high
speed (mach 3) interceptor and escort fighter for the B-70 "Valkyrie" bomber
under development at the same time. The delta wing Rapier, in its pre-mockup
phase, was to have a canard (forward-mounted pitch-control surface), and
three vertical stabilizers: one on the fuselage centerline a a pair at the
halfway point on the wing trailing edge for high speed stabilization at
speeds above mach 2.

The aircraft design was changed during the mockup phase. The canard was
removed and the upper portions of the wing-mounted vertical stabilizers were
removed. The wing was changed from a standard delta to a double-delta; the
winglet incorporated a droop and 45 degree sweep (the main wing had about a
65 degree sweep).

The F-108 program was canceled on 23 September, 1959 never getting past
the mockup phase.

The 1950s and 1960s saw the
J93, the first engine to operate at Mach 3, power the experimental XB-70
bomber; a nuclear-powered turbojet; and the addition of a fan to the rear of
the CJ805 to create the first turbofan engine for commercial service for the
Convair 990. In August 1965, the Air Force picked GE's TF39 to power its C-5
Galaxy cargo plane. This was the world's first high bypass turbofan to enter
service. Another success of the period was the J85 turbojet engine that
powered the Northrop F-5 Freedom Fighter, which was used by more than 30
nations.

Click on Picture to enlarge

General Electric J93-GE-3 turbojet

The General Electric J93 turbojet engine was designed as the powerplant
for both the North American XB-70A Valkyrie bomber and the North American XF-108
Rapier interceptor. The J93 was a single-shaft axial-flow turbojet with a
variable-stator compressor and a fully-variable convergent/divergent exhaust
nozzle. The maximum sea-level thrust was 31,500 pounds.

The J93 engine was ready before either the XB-70A or the XF-108 were, so
the Air Force concluded that the engine should be initially flight tested in an
existing aircraft. B-58A serial number 55-662 was selected for the project, and
on July 1, 1959, Convair began the modification of the aircraft so that it could
accept the installation of a J93 engine in a specially-modified underfuselage
pod. Following the completion of the Convair modifications, the aircraft was
delivered to General Electric's Edwards AFB operation as a NB-58A. While there,
a J93-GE-3 engine was installed in a special underfuselage pod.

Unfortunately, the F-108 interceptor was cancelled outright and the B-70
project was reoriented to a research project only. A few NB-58A ground runs were
made with the J93 engine in place, but the day before the first flight was
scheduled to take place, the funding for the NB-58A project was cancelled.
Consequently, the NB-58A/J93 combination never took to the air. The special pod
was removed from the NB-58 testbed, and the NB-58A itself was converted to a
TB-58A and later flew chase missions for the XB-70A at Edwards AFB. It was
consigned to storage at MASDC in 1970, and eventually scrapped in 1977.

E-mail from Jennifer Raabe, with information and confirmation that
NB-58A flight tests with J93 engine never actually took place.

An
Interceptor ahead of its time

By Erik Simonsen

Click on Picture to enlarge

During the early 1950s, as strategic planners at North
American Aviation were surveying requirements for the next decade, two
significant advanced concepts began to emerge.

One was a Mach 3+ intercontinental bomber, later designated
the XB-70 Valkyrie, the other a long-range Mach 3+ interceptor that could
protect the entire North American continent from intruders carrying nuclear
arms.

In November 1955, the U.S. Air Force awarded study
contracts to NAA, Lockheed and Northrop after the completion of a Phase I
advanced interceptor competition initiated during September of that year.

NAA was awarded the development contract on June 1, 1957,
for what was officially known as Weapons System 202A. Designated the F-108, a
full-scale mockup was completed and on January 20, 1959, presented to the Air
Force. Named Rapier in May 1959, and slightly preceding the development of the
XB-70, the Department of Defense and NAA considered the F-108 a significant
technological leap.

Ambitious as the project was, NAA felt the development of
the advanced interceptor was well within its capabilities. With unmatched mass
production credentials, NAA had developed the first operational supersonic
fighter, the F-100, and was concurrently developing the Mach 2 A-3J Vigilante
(later RA-5C) for the Navy.

As a cost-saving measure while developing the F-108, NAA
instituted a program of shared technologies with the proposed XB-70. The
interceptor would incorporate the same basic 30,000-pound-thrust YJ-93 engine,
honeycomb stainless steel materials and clamshell escape systems as the XB-70.
The F-108 also could be utilized as an escort for the B-70.

Operating at Mach 3 at 75,000 feet (and zoom climbing to
100,000 feet), the Rapier would have provided U.S. air defenses an effective
look-down-shoot-down capability, intercepting potential adversaries with nuclear
arms well away from U.S. borders.

While air defense was considered top priority within some
circles, U.S. defense budgets began to flow in favor of intercontinental
ballistic missile development.

As a result, NAA's fighter legacy would come to an end on
September 23, 1959, with a statement from the Air Force announcing that the
F-108 program was being canceled. This decision resulted in a domino effect by
immediately negating the shared technology program and dramatically increasing
the cost of the embryonic XB-70—a factor leading to its eventual cancellation.

No Rapiers would be built, and its advanced AN/ASG-18 radar
system and funding soon would be transferred to the classified Lockheed
YF-12A/F-12B. Yet, surprisingly, in 1968 the promised F-12B Mach 3+ interceptor
also was canceled, twice leaving the United States without a high-technology air
defense fighter.

The U.S. strategy of nuclear intercontinental ballistic
missile parity with the Soviet Union was reflected in the eventual selection of
the F-106 Delta Dart as the nation's top air defense fighter. Though it was an
excellent aircraft, its Mach 2.3 supersonic performance in afterburner was
limited to about 12 minutes. The rationale for a Mach 3+ interceptor had been to
meet threatening nuclear-armed bombers quickly, keeping any fallout from
jettisoned ordnance or premature detonations far from the United States. The
F-108 would have intercepted targets a thousand miles from its base.

Fortunately, during the Cold War the Soviet bomber force
did not evolve into an overwhelming threat—and the delayed supersonic Tupolev
Tu-160 Blackjack achieved limited production.

Courtesy Of The Boeing
Company

The F-108A Rapier

By Greg Goebel / Public
Domain

One of the interesting footnotes to the XB-70 program was
that technology developed for the XB-70 was to also be applied to a huge
long-range interceptor / escort fighter named the "F-108A Rapier". The F-108 had
the sole distinction of being the last fighter project worked on by North
American.

The Rapier project was initiated by the USAF in October
1955, originally under the designation of "Long Range Interceptor / Experimental
(LIRX)", leading to the award of a contract to North American in June 1957 for
two F-108A prototypes. The F-108A would have Mach 3 performance and range
adequate to intercept Soviet bombers flying over the North Pole to attack North
America, and was also considered as an escort for the B-70. The Air Force hoped
to have the F-108A in service by 1963, and contemplated buying hundreds of them.

The F-108A was to be a two-seat aircraft, powered by twin
J93 engines and armed with advanced Falcon missiles. It evolved through a number
of configurations, converging on a design implemented in a mock-up unveiled in
January 1959. The type received the name "Rapier" in May of that year.

As the F-108A was conceived at that time, it looked
something like the fuselage of the North American "Vigilante" carrier-based
bomber, then in flight test, mated to a high-mounted delta wing with drooping
wingtip panels, featuring a single tall vertical tailplane on the end of the
fuselage and a smaller vertical tailplane under the middle of each wing.

The crew were to set in tandem seats fitted with ejection
capsules for high-speed escape. The Rapier was to be armed with three GAR-9
advanced Falcon long-range air-to-air missiles, directed by the aircraft's
powerful AN/ASG-18 radar.

Initial flight of the first prototype was scheduled for the
spring of 1961, but the USAF was already having second thoughts. The Soviet
nuclear force was moving towards ICBMs, and an expensive dedicated long-range
interceptor didn't seem like it was worth the money any more.

The Rapier program was cancelled in September 1959. The
GAR-9 (later AIM-47A) missile and the AN/ASG-18 were later used with the
Lockheed YF-12A, which was essentially an experimental interceptor version of
the famed Lockheed "SR-71 Blackbird" reconnaissance aircraft. The YF-12A never
got out of the prototype stage.

North American XF-108 Rapier

By Joe Bauger

Click on Picture to enlarge

The F-108A Rapier was destined to be the last fighter project carried out
by North American Aviation, builders of such immortals as the P-51 Mustang and
the F-86 Sabre.

The F-108 project was originally known as the LRIX (Long-Range
Interceptor, Experimental) and was initiated by the Air Force on October 6,
1955. On June 6, 1957, North American was issued a letter contract for two
prototypes of a long-range, high-performance interceptor to be designated
F-108A. The company designation for the aircraft was NA-257. It was to be
capable of Mach 3 performance and was intended to serve as a long-range
interceptor that could destroy attacking Soviet bombers over the poles before
they could get near US territory. It was also to serve as the escort fighter for
the XB-70 Valkyrie Mach-3 strategic bomber, also to be built by North American.
The Air Force expected that the first F-108A would be ready for service by early
1963. An order for no less than 480 F-108s was anticipated.

The F-108A design that North American ultimately produced called for a
large delta-winged aircraft powered by a pair of afterburning General Electric
J93-GE-3AR turbojets fed by variable inlets mounted underneath the wing roots.
The F-108 aircraft was designed for a maximum speed of 1980 mph at 75,550 feet
and for a 1020-mile combat radius. The pilot and radar operator sat in tandem
individual ejector capsules in the forward cockpit. The aircraft was to be
equipped with an extremely sophisticated avionics system, directed by the Hughes
AN/ASG-18 search and tracking radar which was to have a range of over 100 miles.

The F-108A was to be armed with three advanced Hughes GAR-9 Falcon
missiles housed in an internal weapons bay. The GAR-9 missile was powered by a
Lockheed storable liquid-propellant rocket motor which was capable of driving
the missile to hypersonic speeds of up to Mach 6 and achieving ranges of up to
115 miles. The GAR-9 missile used semi-active radar homing for midcourse
guidance, with passive infrared homing being used for the final run-in to the
target.

A mockup was inspected in January 1959, with the initial flight being
planned for March 1961. The popular name *Rapier* was assigned on May 15, 1959.

However, by mid 1959, the Air Force was already beginning to experience
some doubts about the high cost of the Rapier program. The primary strategic
threat from the Soviet Union was now perceived to be its battery of
intercontinental ballistic missiles instead of its force of long-range bombers.
Against intercontinental ballistic missiles, the F-108A interceptor would be
completely useless. In addition, the Air Force was increasingly of the opinion
that unmanned intercontinental ballistic missiles could accomplish the mission
of the B-70 Valkyrie/F-108 Rapier combination much more effectively and at far
lower cost. Consequently, the F-108A project was cancelled in its entirety on
September 23, 1959, before any prototypes could be built. The XB-70 project was
also halted, and on December 3, 1959 was cut back to only one prototype.

The work on the Rapier did not entirely go to waste. The work that Hughes
did on the AN/ASG-18 radar was later transferred over to the Lockheed YF-12A
interceptor project, and the GAR-9 Falcon (redesignated AIM-47A in 1962) missile
originally developed for the F-108A was used to arm the YF-12A.

By Joe Bauger

Click on Picture to enlarge

The F-108 Rapier was North American Aviation's
answer to DOD cutting edge interceptor criteria issued in the mid-Fifties and
envisaged as countering all airborne threats in the post 1962 world. A complete
weapons system, as were other members of the "Century Series", the F-108 was to
eventually supplant the F-106 by operating independently, well beyond the limits
of the then standard SAGE (Semi-Automatic Ground Environment) air intercept
system. The Rapier was designed to "run with the big dogs," at Mach 3 and to
zoom climb altitudes in excess of 100,000 feet. Manned by two aircrew members in
a tandem cockpit, powered by two brutish J93 General Electric engines (six of
which powered the XB-70), the cranked delta-winged Rapier was some fifteen feet
longer and slightly heavier than the F-111. Missiles only were the order of the
day, and the F-108 carried three AIM 47 Falcons on a rotary launcher in the
weapons bay.

The project moved along smartly, with a full scale mockup finished, the first
flight scheduled for 1961 and Initial Operating Capability (IOC) estimated in
1963. Although the project was on schedule with few, if any, developmental
glitches, the USAF suddenly announced in September 1959 that the F-108 was
canceled "because of a shortage of funds and priorities....." "Priorities" seems
to be the operative word, since an apparently unknowing North American design
team was running against a parallel "Black World" ultra project which was to
become the YF-12. Interestingly, the Hughes radar and AIM 47s appeared on the
Lockheed Blackbird!